This paper presents a numerical study of cryogenic fluid flow cavitation in a microchannel and annulus, with forward‐facing step. Two‐phase mixture model is used to simulate the effects of magnetic fields produced by an electrical wire and magnetic doublet on the cavitation region. The results show that considerable reduction of vapor generation due to pressure drop is possible in the presence of an external magnetic fields. This phenomenon occurs due to effect of magnetic field on the pressure distribution in the contraction region and it is observed in both types of studied magnetic fields.